A “gobo” is a metal, normally stainless steel, or glass disk, in which a pattern or shape is formed to produce a light pattern when the gobo intercepts a light beam. Each gobo is normally fitted releasably inside a first seat in a gobo support of the type described in U.S. Pat. No. 5,401,326, and the gobo support is in turn fitted to the gobo carrier wheel, inside a second seat. More specifically, as described in U.S. Pat. No. 5,401,326, each gobo support is riveted to the gobo carrier wheel, so, to change the gobos, they must be extracted axially from the respective supports, which, given the limited amount of space available axially in a lighting fixture, can prove awkward.
To eliminate this drawback, two technical solutions for gobo support assemblies have been proposed, in which the gobo supports are fitted in selectively releasable manner inside the respective second seats on the respective gobo carrier wheels. The two solutions are similar, and are disclosed in Patent Applications US 2002/0075685 and WO 2004/046607 respectively.
In a first solution disclosed in Patent Application US 2002/0075685, the gobo support is inserted at least partly inside the second seat, which is defined by a hole formed in a plate of the gobo carrier wheel; and the gobo support is retained inside the hole by a leaf spring which acts on a gobo support flange resting on one edge of the plate.
A second solution disclosed in Patent Application WO 2004/046607 differs from the first by the gobo support having at least two projections, and by the second seat comprising, in addition to the main hole, two auxiliary holes engaged axially by the projections. In this case, too, the projections are retained inside the respective seats by a leaf spring which acts on a gobo support flange resting on the plate.
Functionally speaking, both the above solutions involve extracting and inserting the gobo supports parallel to the gobo carrier wheel axis, and so require room for manoeuvring.
Using either of the above solutions, the axial space allowed in the stage lighting fixture for the gobo support assembly must therefore equal the axial size of the gobo support assembly plus the manoeuvring space required to insert and extract the gobo supports.
A technical solution that partly solves the problem is described in the 1999 Manual of the Società Coemar S.p.A. CP 1200 Hard Edge stage lighting fixture, available on-line at http.com/Pages/Manual_fix.htm.
Coemar S.p.A. adopted a similar technical solution in their NAT 4000 lighting fixture of 1997, the manual of which can be found on the above web page.
Pages 28 and 29 of the CF 1200 Hard Edge manual describe a gobo support assembly comprising a gobo carrier wheel that rotates about an axis and comprises a plate perpendicular to the axis of rotation, and interchangeable gobo supports. Each gobo support comprises a wedge-shaped flange that fits inside a seat formed inside pins mounted on the base plate; and the gobo support is held in a given position inside the second seat by a spring, which has a first end hinged to the plate, and a second end that hooks onto a projection on the base plate.
Though involving no axial movement to insert and extract the gobo supports, this solution has the drawback of having to detach and reattach the spring whenever a gobo support is extracted and inserted respectively. Moreover, given the axial distance of the gobo support seat, the “axial” size of the gobo support assembly is considerable.
Since the gobo supports are changed entirely by hand by an operator, the tight space available inside the lighting fixture makes it difficult to position the gobo support correctly and to detach and reattach the spring.